The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Ethanol, also know as ethyl alcohol, is a flammable, colorless chemical compound that can be mixed with gasoline to fuel an internal combustion engine. Flexible fuel vehicles include adaptations that allow the vehicle to run on various blends of gasoline and ethanol. For example, E85 fuel contains a mixture of 85% ethanol and 15% gasoline. A virtual flex fuel sensor and method detects the concentration of ethanol in the fuel. Based on the concentration level, the air/fuel ratio is adjusted and the engine operation is controlled accordingly.
During the combustion process, gasoline and ethanol are oxidized and hydrogen (H) and carbon (C) combine with air. Various chemical compounds are formed and released in an exhaust stream including carbon dioxide (CO2), water (H2O), carbon monoxide (CO), nitrogen oxides (NOx), unburned hydrocarbons (HC), sulfur oxides (SOx), and other compounds. However, the use of ethanol in the fuel reduces the amount of carbon dioxide (CO) and nitrogen oxides (NOx) in the exhaust.
Automobile exhaust systems include a catalytic converter that further reduces the levels of CO, HC, and NOx in the exhaust gas by chemically converting these gasses into carbon dioxide, nitrogen, and water. Diagnostic regulations require periodic monitoring of the catalytic converter for proper conversion capability. Typical monitoring methods employ two exhaust gas oxygen sensors and infer the conversion capability of the catalytic converter using the sensor signals. One sensor monitors the oxygen level associated with an inlet exhaust stream of the catalytic converter. This inlet O2 sensor is also the primary feedback mechanism that maintains the fuel-to-air (F/A) ratio of the engine at the chemically correct, or stoichiometric F/A ratio needed to support the catalytic conversion processes. A second or outlet O2 sensor monitors the oxygen level concentration of the exhaust stream exiting the catalytic converter. Excess O2 concentration in the exiting exhaust stream induces a “lean” sensor signal. A deficit or absence of O2 in the exiting exhaust stream induces a “rich” sensor signal.
Traditional catalytic converter monitoring methods relate the empirical relationships that exist between the inlet and outlet O2 sensor to quantify catalyst conversion capability. These methods compare sensor amplitude, response time, response rate, and/or frequency content data. All of these measurements are affected by a property of a catalytic converter known as Oxygen Storage Capacity (OSC). OSC refers to the ability of a catalytic converter to store excess oxygen under lean conditions and to release oxygen under rich conditions. The amount of oxygen storage and release decreases as the conversion capability of the catalytic converter is reduced. Therefore, the loss in OSC is related to the loss in conversion capability.
Methods and systems for monitoring a catalytic converter based on the OSC are described in commonly assigned U.S. Pat. No. 6,874,313. The methods and systems relate to various types of hydrocarbon fuels. As implemented, the methods and systems may not properly diagnose a catalytic converter for engine systems running alternative fuels such as E85 or diesel.